Photodiode technology relies on two key parameters.
The first parameter is the sensitivity of the photodiode, which represents the capacity of the photodiode to collect photogenerated charge carriers. This parameter controls the intensity of the current generated for a given illumination.
The second parameter is the dark current, which represents the current flowing through the photodiode when no light illuminates the photodiode. This parameter controls the difference in intensity of the current generated for a given difference in illumination.
A relatively large portion of the electrons generated in the photodiode do not contribute to the photocurrent as they are trapped by structural defects or recombination zones.
In the case of photodiode matrix sensors, deep isolation trenches are employed so as to limit the neighboring effects. However, deep isolation trenches may play a similar role to structural defects or recombination centers. This is because deep isolation trenches generally comprise an insulating material and are produced in a semiconductor medium. Moreover, an inherent property to silicon/oxide or silicon/nitride interfaces is to have a positive surface charge capable of attracting the photogenerated electrons. It will therefore be understood that deep isolation trenches act as traps for the photogenerated electrons.
A number of studies have been carried out addressing problems of the interface between insulator and semiconductor, particularly in structures similar to photodiodes. The following documents will be considered in order to illustrate the prior art.
The document “SiN/SiC:H passivation layers for p and n type Si wafers”, by U. Coscia et al., Thin Solid Films, 516, 1569 (2008), the disclosure of which is hereby incorporated by reference, describes the effects of surface charges of certain materials used for passivation in microelectronics. In particular, the following structures are mentioned: Al/SiNx/Si; Al/a-SiCx:H/Si; and Al/SiNx/a-SiCx:H/Si.
As may be seen, the deep isolation trenches may have recombination effects, in which the photogenerated electrons and the charges at the interface between the deep isolation trenches and the silicon in a photodiode recombine.
The document “Development of robust interfaces based on crystalline γ-Al2O3(001) for subsequent deposition of amorphous high-κ oxides” by C. Merckling et al., Microelectronics Engineering, 84, 2243-6 (2007), the disclosure of which is hereby incorporated by reference, describes processes for the growth of crystalline γ-Al2O3 structures intended for the subsequent growth of high-κ oxides.
The document “Evidence of a high density of fixed negative charges in an insulation layer compound of SI” by D. Konig et al., Thin Solid Films 285, 126 (2001), the disclosure of which is hereby incorporated by reference, describes the formation of a structure capable of generating a negative bias effect in a silicon structure. In particular, it mentions the effect of associating a layer of aluminum fluoride/silicon dioxide alloy on silicon which makes it possible for negative charges at the interface between the two layers of materials to appear.
Thus, it may be seen that there are materials capable of creating a layer of negative charge at the interface with silicon.
There is therefore a need to have a production process for minimizing or eliminating the trapping of photogenerated electrons near deep isolation walls.
There is also a need for a device of the photodiode type in which the trapping of the photogenerated electrons near the deep isolation walls is minimized or eliminated.